It is the current practice in packaging insulated communication wire to coil the wire in a figure 8 configuration of the coil which is used to reduce twisting of the wire as it is coiled, thereby reducing a tendency of the wire to kink as it is pulled from the carton, generally through an opening in a side wall thereof. The pulling process is facilitated by the installation of a payout tube which extends into the interior of the carton, and which is affixed to a wall thereof in a suitable manner so as to have a stub portion extending outside of the carton. In U.S. Pat. No. 5,152,476 of Moser, there is shown a preferred arrangement for affixing the tube to the wall of the carton having a modified bayonet lock type of action. Numerous prior art arrangements utilize this arrangement, or modifications thereof, for mounting the tube.
Most tubes in use today are in the form of hollow elongated cylinders with the ends thereof being radiused between the outer and inner walls to eliminate sharp corners over which the wire passes as it is pulled through the tube. Such radiused ends are shown in U.S. Pat. Nos. 5,064,136 and 5,115,995 of Hunt. In these arrangements, the entrance end surface substantially conforms to a hemi-toroidal surface having a faired joinder at its inner and outer margins with the inner and outer walls of the tube. Such a rounded surface imposes a lower limit on the bend radius of the wire being pulled through the tube, which however, does not prevent kinking of the wire or damage to its insulation when the wire is being pulled from layers immediately adjacent to the tube and lying between the end of the tube and the wall in which the tube is mounted. In that case, the wire undergoes a sharp reverse bend as it enters the tube, and the radiused end of the tube is insufficient to prevent kinking and possible damage.
The aforementioned Moser patent discloses an end cap for the entrance end of the payout tube which greatly increases the minimum possible radius of curvature of the wire, thereby materially reducing the tendency of the wire to kink even in the extreme reverse bend case discussed in the foregoing. The cap of the Moser patent has, at its entrance or back end an annular flange, the surface area of which conforms to approximately one cross-sectional quadrant of a toroidal surface having a radius of sufficient magnitude that when the wire is bent to pass over the surface in contact therewith, it will not kink. The toroidal surface of the cap is faired into a flat surface, the plane of which is substantially normal to the axis of the cap, and which borders the wire passage interior cylindrical wall surface of the cap. In use, the hollow cylindrical payout tube is mounted in the carton, and the cap is affixed to the entrance end, ie., the interior or rear end. The wire being payed out cannot be bent to a radius less than the radius of the flange, even for a complete reverse bend, except where the wire passes into the payout tube. At the region where the cap joins the payout tube, there remains a relative small radiused surface over which the wire passes, which allows the wire to be bent to a radius that is too small to prevent kinking, i.e., the radius is less than the critical radius R.sub.c, below which kinking can occur.
Any cap arrangement for the payout tube gives rise to the additional problem of the introduction of a separate part, with the possibility of its being lost or mislaid. Also, the fabrication of such a separate part requires additional molds and fabrication steps, thereby increasing the cost of the payout tube assembly. Moser apparently recognizes the problem at least to some extent, by suggesting that the cap and the payout tube may be fused together to produce a single unitary structure, but apparently the two parts are intended to be fabricated separately and then joined, with a consequent two molding operations, hence, an increase in production costs.
In U.S. Pat. No. 5,520,347 of Bass et al. there is disclosed a one-piece payout tube which overcomes the aforementioned disadvantages of the Moser device as well as many other prior art devices. The Bass et al. (hereinafter "Bass") payout tube has a flange at the cable entrance end thereof which has a radiused surface, the radius being greater than the kinking radius R.sub.c, and a central opening where the radiused surface fairs into the inner wall of the tube, with the inner wall being tangential to the radiused surface. The opposite or cable exit end of the tube has a mounting arrangement which is strengthened by suitable ribs and strength members, which are cast or formed integral with the remainder of the tube. The Bass patent is incorporated herein by reference.
There has been an increase in the use of cable having low smoke or flame resistant characteristics wherein, for the most part, the cable is jacketed with a low smoke material such as low smoke polyvinylchloride (PVC). Unfortunately, cables jacketed with such material display a greater tendency to kink than cables jacketed with other materials due to the additives in the PVC which reduce cable flexibility, with a consequent increased tendency to damage the insulation, and, in the extreme, possibly the wire itself. The aforementioned Bass arrangement does successfully minimize normally occurring kinking, but, especially where low smoke PVC is used as the insulating material, it is possible for some kinking to occur.
In use, a payout tube functions to guide cable out of the carton in, preferably, an unkinked condition, with a reasonable ease of payout. However, it is seldom the case that all of the cable contained in a carton is payed out at one time, i.e., in a single operation, and usually, after the desired length of cable has been pulled out, the cable is cut. When this occurs, the cable, which has been under tension, tends to spring back into the carton where it becomes inaccessible in the extreme case. Numerous arrangements have been used to prevent the cable from thus springing back, and for holding it fixed within the tube. One arrangement common in the prior art and shown in the Bass patent is a resilient diaphragm formed of wedge-shaped fingers adjacent the cable entrance end of the tube. The fingers are resilient enough to yield to the cable as it is pulled out under tension, but sufficiently stiff enough to resist the tendency for the cable to spring back after being cut, thereby holding the cable in place provided the spring back action is not too strong. U.S. Pat. No. 5,152,476 of Moser, U.S. Pat. No. 5,064,136 of Hunt and U.S. Pat. No. 4,274,607 of Priest all show such diaphragm arrangements. Provided cable tension is not excessive, such diaphragms perform adequately, but, as is the usual case, being integrally formed with the tube, they require complex mold designs which materially increase costs. An inherent disadvantage to such diaphragms is their tendency to prevent the cable that is being pulled out from untwisting. This can lead to a buildup of twist tension within the carton which, in turn, can lead to tangling or, worse, to knotting. Diaphragms also place a limit on the material from which the tube is made. For the diaphragms to work at all, they must be made of a resilient material such as polyethylene, and cannot function properly if made of a stiffer material such as a polycarbonate. Another arrangement in the prior art is an end cap which is designed to fit over the exit end of the tube, or a plug that fits into the exit end and which, in either case, pinches the cable against the tube to affix it in place. Such caps or plugs are easily misplaced or lost, and thus there is a built in unreliability in their use.
In virtually all of the payout arrangements of the prior art, difficulty in achieving smooth, regular payout is encountered at lower temperatures where the cable becomes stiff and difficult to handle. Inasmuch as payout at lower temperatures is common, an arrangement which provides smooth payout at low temperatures is highly desirable